Separation science and purification are well known in the art and two journals dedicated to this field are "Separation Science and Technology" and "Separation and Purification Methods", both published by Marcell Dekker, N.Y., N.Y. Numerous books dedicated to this topic are also well known in the art. Eventually, the chemical practitioner needs to rely on one or more separation and/or purification methods involving sorption techniques. These techniques provide a means comprising a sorptive medium for resolving (i.e., separating and analyzing) mixtures by selectively sorbing and desorbing components in the mixture.
Recently sorptive media in a polytetrafluoroethylene (PTFE) matrix have been described in separation science.
U.S. Pat. No. 4,810,381 and related U.S. Pat. Nos. 4,906,378 and 4,971,736 describe a composite chromatographic article comprising a polytetrafluoroethylene fibril matrix, and non-swellable sorptive particles enmeshed in the matrix.
U.S. Pat. No. 4,153,661 discloses a method of making a polytetrafluoroethylene composite sheet comprising a PTFE matrix with substantially water insoluble particulate materials dispersed therein. The resulting sheet is extremely pliable, akin to doe skin. It is said to be useful as an electronic insulator or a semi-permeable membrane.
U.S. Pat. No. 4,373,519 teaches a composite wound dressing comprising a PTFE matrix with water-swellable hydrophilic absorptive particles enmeshed in the matrix, and, optionally, a partially occlusive film coated on one surface of the matrix. The sheets are described as conformable and chamois-like.
U.S. Patent Nos. 4,565,663 and 4,460,642, which are related to U.S. Pat. No. 4,373,519 (a division of a continuation-in-part application and a continuation-in-part, respectively) disclose water-swellable composite sheets having a PTFE matrix in which are enmeshed water-swellable hydrophilic absorptive particles. The sheets are described as conformable and chamois-like. Certain water-swellable cation exchange resins in the composite sheets can be used as chromatographic materials.
U.S. Pat. Nos. 4,722,898 and 4,871,671 disclose a composite article comprising a polytetrafluoroethylene fibril matrix in which are enmeshed viable animal, bacterial, fungal, or yeast cells.
The background art taught several formulations for blending an aqueous PTFE dispersion with various additives and/or adjuvants, designed for specific purposes. The background art also taught that blending of these particles or additives with an aqueous PTFE dispersion to form a mass having a putty-like or dough-like consistency and only specified addition of sufficient lubricant to exceed the sorptive capacity of the particles (see e.g., U.S. Pat. No. 4,810,381, column 6, lines 22-30; see also U.S. Pat. Nos. 4,373,519, 4,460,642 and 4,565,663). Moreover, U.S. Pat. No. 4,810,381 provides a guide and a caution when sorptive capacity is exceeded (see col. 6, lines 25-33).
U.S. Pat. Nos. 3,407,096, 3,407,249, and 3,556,161 teach incorporation of extractable or leachable organic and inorganic filler particles at various levels and particle sizes in composite sheets to provide the desired porosity for their applications. U.S. Pat. Nos. 3,864,124, 4,194,040, 3,383,092, 3,005,795, and 3,533,930 teach dry or lubricant-free processes. U.S. Pat. No. 3,281,511 describes use of leachable filler particles (colloidal alumina, sodium chloride, and ammonium carbonate), which are removed after making the article, to create porosity by an extraction/leaching method. In addition, the resulting fibrillated matrix is PTFE and does not contain sorptive particulate for separation purposes.
U.S. Pat. No. 3,315,020 and GB 993,193 teach preparation of PTFE sheeting by an extrusion process and then performing rolling or stretching. Lubricant fluid which will mix with polytetrafluoroethylene, e.g., naphtha, gasoline, kerosene, alcohols, glycerol, and most organic liquids can be used and up to 50 volume percent filler. The sheeting is used to mold shaped articles.